I think what he means is, he's got the program set to something like full screen desktop or whatever and the program is automatically sized to 800x600 on his computer but 1024x768 on another computer
Dude go into settings on the project manager and specify a resolution OR just use set display mode x,y,bitdepth
But the better way is to use percentage values rather than actual values for example if you need to place a HUD in the centre down the bottom of the screen you'd use something like
paste sprite 1,(screen width()/2)-(sprite width(1)/2),screen height()-sprite height(1)
So if thats a little complicated this is how it works, lets assume you have an image thats 100x50 and your resolution is 800x600, it'll put the image at 400(800/2) - 50(100/2) = 350. The image is 100 pixels wide so it'll stretch from 350-450 which is exactly in the middle
If you then change resolution to say 640x480 it'll be placed at 270 to 370 again in the middle but it'll look larger in lower resolutions smaller in higher resolutions, you can make it stretch/shrink to look the same size in any resolution but I won't explain that now
